Classical galactosemia, the clinical syndrome of failure to thrive, cataracts, galactosuria, liver disease and mental retardation, is most often caused by a severe deficiency, but not usually total absence of the enzyme galactose-1-phosphate uridyltransferase (GALT). In addition to eliminating dietary galactose in the treatment of galatosemia, there are clinical and theoretical arguments for augmenting residual GALT activity for protection against mental retardation or more subtle cumulative toxicities. This research proposes to study the molecular basis for two recently identified methods of increasing GALT activity: perfusion of suckling rat liver with galactose and folic acid treatment of suckling rats. The molecular mechanisms responsible for stimulated GALT activity will be examined by the analysis of in tissue specific microheterogeneity of GALT. This will involve 1) defining the variety of tissue specificity of GALT isozymes by isoelectric focusing; 2) following quantitative and qualitative changes in the GALT isozyme patterns in the folate treated rat and in the in situ liver perfusion with carbohydrate solutions; 3) determining the specific post-translational modifications of GALT using a variety of chemical and enzymatic approaches; 4) purifying selected GALT isozymes for detailed kinetic and chemical studies. Together these studies will add to our knowledge of the molecular biology of GALT and mechanism for the specific enhancement of GALT activity in the treatment of galactosemia.